使用 Jettison 在 Java 中从 JSON 到 DOM

Question

到目前为止，这是一个失败的故事，欢迎提出任何建议。我尝试了以下方法：

使用带有 Saxon 的 JAXP 到 XMLStreamReader 到文档

代码：

JSONObject obj = new JSONObject("{\"alice\":{\"bob\": \"a\"}}");
AbstractXMLStreamReader reader = new MappedXMLStreamReader(obj);

StAXSource source = new StAXSource(reader);
Document document = XMLUtils.createDocument();
DOMResult result = new DOMResult(document);
Transformer identity = TransformerUtils.getIdentityTransformer();
identity.transform(source, result);
result.getNode();

这会失败，因为我们使用的 Saxon 转换器不支持 StAXSource。例外是：

org.orbeon.saxon.trans.DynamicError: A source of type javax.xml.transform.stax.StAXSource is not supported in this environment
    org.orbeon.saxon.event.Sender.send(Sender.java:185)
    org.orbeon.saxon.IdentityTransformer.transform(IdentityTransformer.java:29)
    org.orbeon.oxf.xml.TransformerWrapper.transform(TransformerUtils.java:597)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:93)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

使用带有 Xalan 的 JAXP 到文档的 XMLStreamReader

代码：

JSONObject obj = new JSONObject("{\"alice\":{\"bob\": \"a\"}}");
AbstractXMLStreamReader reader = new MappedXMLStreamReader(obj);

StAXSource source = new StAXSource(reader);
Document document = XMLUtils.createDocument();
DOMResult result = new DOMResult(document);
Transformer identity = orbeon.apache.xalan.processor.TransformerFactoryImpl.newInstance().newTransformer();
identity.transform(source, result);
result.getNode();

Xalan 2.5.1（我们正在使用的版本）会失败。最新版本是 2.7.1，也许他们在该版本中添加了对 StAXSource 的支持。

javax.xml.transform.TransformerException: Can't transform a Source of type javax.xml.transform.stax.StAXSource
    orbeon.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:372)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:82)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

使用 XMLEventWriter 和 DOMResult 的 XMLStreamReader 到文档

代码：

JSONObject obj = new JSONObject("{\"alice\":{\"bob\": \"a\"}}");
AbstractXMLStreamReader streamReader = new MappedXMLStreamReader(obj);
XMLInputFactory readerFactory = XMLInputFactory.newInstance();
XMLEventReader eventReader = readerFactory.createXMLEventReader(streamReader);

Document document = XMLUtils.createDocument();
DOMResult result = new DOMResult(document);
XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
XMLEventWriter eventWriter = outputFactory.createXMLEventWriter(result);
eventWriter.add(eventReader);
eventWriter.close();

result.getNode();

这会导致 Xerces 中的 NPE：

java.lang.NullPointerException
    orbeon.apache.xerces.dom.CoreDocumentImpl.setXmlVersion(CoreDocumentImpl.java:850)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    com.sun.xml.internal.stream.writers.XMLDOMWriterImpl.writeStartDocument(XMLDOMWriterImpl.java:583)
    com.sun.xml.internal.stream.writers.XMLEventWriterImpl.add(XMLEventWriterImpl.java:96)
    com.sun.xml.internal.stream.writers.XMLEventWriterImpl.add(XMLEventWriterImpl.java:72)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:95)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

使用 XMLEventWriter 和 Writer 将 XMLStreamReader 转换为文档

代码：

JSONObject obj = new JSONObject("{\"alice\": {\"bob\": \"a\"}}");
AbstractXMLStreamReader streamReader = new MappedXMLStreamReader(obj);
XMLInputFactory readerFactory = XMLInputFactory.newInstance();
XMLEventReader eventReader = readerFactory.createXMLEventReader(streamReader);

StringWriter stringWriter = new StringWriter();
XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
XMLEventWriter eventWriter = outputFactory.createXMLEventWriter(stringWriter);
eventWriter.add(eventReader);
eventWriter.close();

out.print(stringWriter.toString());

在 Java 5 中，它会寻找找不到的 com.bea.xml.stream.MXParserFactory：

javax.xml.stream.FactoryConfigurationError: Provider com.bea.xml.stream.MXParserFactory not found
    javax.xml.stream.FactoryFinder.newInstance(FactoryFinder.java:72)
    javax.xml.stream.FactoryFinder.find(FactoryFinder.java:178)
    javax.xml.stream.FactoryFinder.find(FactoryFinder.java:92)
    javax.xml.stream.XMLInputFactory.newInstance(XMLInputFactory.java:136)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:79)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

使用 Java 6，它会导致 Sun 的 XMLEventAllocatorImpl 中的 NPE：

java.lang.NullPointerException
    com.sun.xml.internal.stream.events.XMLEventAllocatorImpl.getXMLEvent(XMLEventAllocatorImpl.java:82)
    com.sun.xml.internal.stream.events.XMLEventAllocatorImpl.allocate(XMLEventAllocatorImpl.java:55)
    com.sun.xml.internal.stream.XMLEventReaderImpl.nextEvent(XMLEventReaderImpl.java:86)
    com.sun.xml.internal.stream.writers.XMLEventWriterImpl.add(XMLEventWriterImpl.java:72)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:85)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

使用 BadgerFishDOMDocumentParser

代码：

ByteArrayInputStream bais = new ByteArrayInputStream("{\"alice\": {\"bob\": \"a\"}}".getBytes());
Document resDOM = new BadgerFishDOMDocumentParser().parse(bais);

这个在 Sun 的XMLEventAllocatorImpl 中给了我们一个 NPE：

java.lang.NullPointerException
    com.sun.xml.internal.stream.events.XMLEventAllocatorImpl.getXMLEvent(XMLEventAllocatorImpl.java:82)
    com.sun.xml.internal.stream.events.XMLEventAllocatorImpl.allocate(XMLEventAllocatorImpl.java:55)
    com.sun.xml.internal.stream.XMLEventReaderImpl.nextEvent(XMLEventReaderImpl.java:86)
    com.sun.xml.internal.stream.writers.XMLEventWriterImpl.add(XMLEventWriterImpl.java:72)
    org.codehaus.jettison.AbstractDOMDocumentParser.parse(AbstractDOMDocumentParser.java:66)
    org.apache.jsp.gaga_jsp._jspService(gaga_jsp.java:79)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

---

Answer 1

JSON 不是 XML - 看起来您正在尝试使用 XML 解析器解析 JSON 对象？ 不过，我可能误解了你的意思。

Answer 2

不，出于某种原因，我认为 Xalan 不支持 Stax。 Saxon 可以，所以你可以试试吗？

但如果没有，也许您应该使用 link text 从 Stax 构建一个 DOM 树，就像 this article 解释的那样？ Xalan 确实接受 DOM 源作为输入。

Answer 3

我也遇到了这个问题，并且经历了和 OP 一样的挫败感。在某处的woodstox 邮件列表中提到了这种行为作为错误。但是，我能够开发一个解决方案。我编写了一个非常基本的 XMLEventReader，它包装了一个 XMLStreamReader，它做得很好。两个重要说明： 1) 此代码按原样提供；具体来说，除了我自己的有限使用之外，我还没有彻底测试过它，2）这个问题在互联网上的其他地方几乎不存在，以及这似乎是 Jettison 应该执行的一个相对基本的操作，强烈建议我，我们正在做一些根本错误的事情，这个解决方案不应该是必要的。用你自己的判断。

首先，这是一个工作的 XMLEventReader：

import java.util.LinkedList;
import java.util.Queue;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.events.XMLEvent;

import com.sun.xml.internal.stream.events.AttributeImpl;
import com.sun.xml.internal.stream.events.CharacterEvent;
import com.sun.xml.internal.stream.events.CommentEvent;
import com.sun.xml.internal.stream.events.DTDEvent;
import com.sun.xml.internal.stream.events.EndDocumentEvent;
import com.sun.xml.internal.stream.events.EndElementEvent;
import com.sun.xml.internal.stream.events.NamespaceImpl;
import com.sun.xml.internal.stream.events.ProcessingInstructionEvent;
import com.sun.xml.internal.stream.events.StartDocumentEvent;
import com.sun.xml.internal.stream.events.StartElementEvent;

public class WorkingXMLEventReader implements XMLEventReader {

    private final XMLStreamReader streamReader;
    private final Queue<XMLEvent> eventQueue = new LinkedList<XMLEvent>();

    public WorkingXMLEventReader (XMLStreamReader streamReader) {
        this.streamReader = streamReader;
    }

    @Override public Object next () {
        try {
            return nextEvent();
        } catch (XMLStreamException x) {
            return null;
        }
    }

    @Override public void remove () {
        throw new UnsupportedOperationException("WorkingXMLEventReader iterator interface does not support remove()");
    }

    @Override public void close () throws XMLStreamException {
        streamReader.close();
        eventQueue.clear();
    }

    @Override public String getElementText () throws XMLStreamException {
        return streamReader.getElementText();
    }

    @Override public Object getProperty (String key) throws IllegalArgumentException {
        return streamReader.getProperty(key);
    }

    @Override public boolean hasNext () {
        try {
            return !eventQueue.isEmpty() || streamReader.hasNext();
        } catch (XMLStreamException x) {
            return false;
        }
    }

    @Override public XMLEvent nextEvent () throws XMLStreamException {
        if (eventQueue.isEmpty())
            parseEvents(eventQueue, streamReader, streamReader.next());
        return eventQueue.remove();
    }

    @Override public XMLEvent nextTag () throws XMLStreamException {
        if (eventQueue.isEmpty())
            parseEvents(eventQueue, streamReader, streamReader.nextTag());
        return eventQueue.remove();        
    }

    @Override public XMLEvent peek () throws XMLStreamException {
        return eventQueue.peek();
    }

    protected static void parseEvents (Queue<XMLEvent> events, XMLStreamReader reader, int type) {
        switch (type) {
        case XMLEvent.START_ELEMENT: 
            events.add(new StartElementEvent(reader.getName()));
            break;
        case XMLEvent.END_ELEMENT: 
            events.add(new EndElementEvent(reader.getName()));
            break;
        case XMLEvent.CDATA:
            events.add(new CharacterEvent(reader.getText(), true, false));
            break;
        case XMLEvent.SPACE:
            events.add(new CharacterEvent(reader.getText(), false, true));
            break;
        case XMLEvent.CHARACTERS: 
            events.add(new CharacterEvent(reader.getText(), false, false));
            break;
        case XMLEvent.ATTRIBUTE:
            for (int n = 0; n < reader.getAttributeCount(); ++ n) {
                AttributeImpl attr = new AttributeImpl(reader.getAttributePrefix(n), 
                        reader.getAttributeNamespace(n), reader.getAttributeLocalName(n), 
                        reader.getAttributeValue(n), reader.getAttributeType(n));
                events.add(attr);
            }
            break;
        case XMLEvent.NAMESPACE:
            for (int n = 0; n < reader.getNamespaceCount(); ++ n) {
                NamespaceImpl ns = new NamespaceImpl(reader.getNamespacePrefix(n), 
                        reader.getNamespaceURI(n));
                events.add(ns);
            }
            break;
        case XMLEvent.PROCESSING_INSTRUCTION:
            events.add(new ProcessingInstructionEvent(reader.getPITarget(), reader.getPIData()));
            break;
        case XMLEvent.COMMENT:
            events.add(new CommentEvent(reader.getText()));
            break;
        case XMLEvent.START_DOCUMENT:
            events.add(new StartDocumentEvent(reader.getEncoding(), reader.getVersion()));
            break;
        case XMLEvent.END_DOCUMENT:
            events.add(new EndDocumentEvent());
            break;
        case XMLEvent.DTD:
            events.add(new DTDEvent(reader.getText()));
            break;
        }   
    }

}

接下来，这里是如何将它用于 OP 的示例：

XMLStreamReader streamReader = new MappedXMLStreamReader(new JSONObject("{\"alice\":{\"bob\": \"a\"}}"));
XMLEventReader eventReader = new WorkingXMLEventReader(streamReader);

Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
XMLEventWriter eventWriter = XMLOutputFactory.newInstance().createXMLEventWriter(new DOMResult(document));
eventWriter.add(eventReader);
eventWriter.close();

// test
Source testSource = new DOMSource(document);
Result testResult = new StreamResult(System.out);
TransformerFactory.newInstance().newTransformer().transform(testSource, testResult);

输出应该是这样的：

<?xml version="1.0" encoding="UTF-8" standalone="no"?><alice><bob>a</bob></alice>

希望对某人有所帮助。